Cellulosic and lignocellulosic structural materials and methods and systems for manufacturing such materials

ABSTRACT

Methods of treating wood and wood products include irradiating untreated wood having a first molecular weight with ionizing radiation to cause an increase in the molecular weight of a cellulosic component of the wood to a second, relatively higher molecular weight.

RELATED APPLICATIONS

This application is a continuation of pending U.S. Ser. No. 13/019,304,filed Feb. 1, 2011, which was a continuation of U.S. Ser. No.12/417,720, filed Apr. 3, 2009. The complete disclosure of each of theseapplications is hereby incorporated by reference herein.

TECHNICAL FIELD

This invention relates to cellulosic and lignocellulosic structuralmaterials, such as wood and wood fiber based composites, and to systemsand methods for manufacturing such materials.

BACKGROUND

Wood is a fibrous tissue, found in the stems of woody plants such astrees and shrubs. According to an article by the University of MinnesotaExtension, wood is generally composed of cellulose (about 50%),hemicellulose (about 15%-25%), and lignin (about 15%-30%).(http://www.extension.umn.edu/distribution/naturalresources/components/6413ch1.html.)

Wood is used in a very wide variety of applications, for example asconstruction materials (including framing lumber, decorative woodwork,flooring, and the like), in boats, toothpicks, gunstocks, cabinets,furniture, sports equipment, and parts for weaving and knitting mills.Moreover, many products are made by processing wood or wood fiber intoother materials. For example, many products are made by dispersing woodfiber in a resin matrix, including composite construction materials suchas beams, particleboard, composite flooring materials, and many otherproducts that are used as substitutes for wood. Other products are madefrom wood layers adhered together, for example plywood and glued woodlaminates such as veneers.

Wood has a number of advantages compared to other materials such asmetal, plastic and concrete. For example, trees are a renewableresource, the cultivation of which offsets carbon emissions andpreserves wildlife habitat. Moreover, wood has aesthetic qualities thatare desirable for many applications, such as flooring and furniture, andexhibits a good strength-to-weight ratio and good resiliency (ascompared, for example to metal or concrete). Wood also generallyexhibits good thermal, sound, and electrical insulating properties.

Different types of wood exhibit different mechanical and aestheticproperties, and have different costs. For example, different types ofwoods exhibit widely different strengths, hardness and flexuralproperties. Softer woods that have a lower flexural modulus generallyare available at lower cost, and may in some cases have desirableaesthetic properties, but are unsuitable for some applications due totheir mechanical properties.

SUMMARY

Many embodiments of this application use Natural Force™ Chemistry.Natural Force™ Chemistry methods use the controlled application andmanipulation of physical forces, such as particle beams, gravity, light,etc., to create intended structural and chemical molecular change. Inpreferred implementations, Natural Force™ Chemistry methods altermolecular structure without chemicals or microorganisms. By applying theprocesses of Nature, new useful matter can be created without harmfulenvironmental interference.

The invention is based, at least in part, on the discovery thatirradiating cellulosic or lignocellulosic materials, for example wood orwood fibers (alone or in a composite or fiber-containing composition),with an appropriate dose of ionizing radiation favorably affects thephysical properties of the materials, for example by increasing themolecular weight and level of crosslinking of at least a cellulosicportion of the wood or fibers. As a result, the mechanical and/or otherproperties of cellulosic and lignocellulosic materials can be favorablyaltered. For example, the flexural modulus and other strength/hardnessproperties of wood and wood fiber containing composites can be increasedby irradiating with ionizing radiation. This increase in modulusimproves the strength-to-weight ratio of the material, and thus allowsthinner, lighter structural members to be used in a given application.In the case of composites, the properties of a part made from thecomposite can be comparable to or better than the properties of asimilar part formed entirely of plastic, providing a significant costsavings. Other properties that are altered are discussed below, andinclude sterilization of the wood or fibers to inhibit fungal growth andresulting deterioration.

In one aspect, the invention features methods of treating wood includingirradiating untreated wood having a first molecular weight and amoisture content of less than about 35% by weight with ionizingradiation to increase the molecular weight of a cellulosic component ofthe wood to a second, relatively higher molecular weight.

Some implementations include one or more of the following features. Thewood can be irradiated multiple times. The energy of the radiation canbe at least 1 MeV. The methods can further include controlling the doseof ionizing radiation to be at least 0.10 MRad. The dose of ionizingradiation can be controlled to a level of about 0.25 to about 2.5 MRad.Irradiating can include irradiating with gamma radiation and/or withelectron beam radiation. Electrons in the electron beam can have anenergy of at least 1.25 MeV, e.g., from about 2.5 MeV to about 7.5 MeV.The methods can further include quenching the irradiated material, insome cases in the presence of a gas selected to react with radicalspresent in the irradiated material. The increase in molecular weight canbe at least 10%, e.g., at least 50%.

In another aspect, the invention features methods of making composites,the methods including combining a matrix material with an irradiatedfibrous material that has been prepared by irradiating a fibrousmaterial including a first cellulosic and/or lignocellulosic materialhaving a first molecular weight to provide a second cellulosic and/orlignocellulosic material having a second molecular weight higher thanthe first molecular weight.

Some implementations may include one or more of the features describedabove, and/or the following features. The matrix materials can include aresin. The fibrous materials can include wood fibers, wood chips, and/orwood particles. The fibrous materials can be irradiated prior to,during, or after combining the fibrous material with the matrixmaterial. The methods can further include curing the matrix material,e.g., during the irradiating step. Irradiating can also be carried outafter curing.

In yet another aspect, the invention features a method that includesirradiating wood that has been injected with a liquid comprising lignin.

Wood that has been irradiated using any of the methods described hereincan be used in construction materials (including framing lumber,decorative woodwork, flooring, and the like), in products made of woodsuch as boats, toothpicks, gunstocks, cabinets, furniture, sportsequipment, and parts for weaving and knitting mills, and in products aremade from wood layers adhered together, for example plywood, parquet,and glued wood laminates such as veneers and laminated beams.Irradiation of laminates can occur before or after lamination isperformed.

The cellulosic or lignocellulosic material can be selected from thegroup consisting of paper waste, wood, particle board, sawdust, silage,grasses, rice hulls, bagasse, cotton, jute, hemp, flax, bamboo, sisal,abaca, straw, corn cobs, corn stover, switchgrass, alfalfa, hay, ricehulls, coconut hair, cotton, seaweed, algae, and mixtures thereof.

The term “untreated wood,” as used herein, refers to wood that is in itsnatural state as harvested, or as harvested and dried. This phrase doesnot include solid wood that has been impregnated with a resin or othermaterial that is not naturally present in the wood.

The term “fibrous material,” as used herein, includes cellulosic andlignocellulosic fibrous materials, e.g., wood fibers, particles andchips and fibers derived from other cellulosic materials such as cornstover and hemp. The fibrous material may be in a natural state and/orprocessed, e.g., delignified.

The full disclosures of each of the following U.S. Patent Applications,which are being filed concurrently herewith, are hereby incorporated byreference herein: Ser. Nos. 12/417,707, 12/417,699, 12/417,840,12/417,731, 12/417,900, 12/417,880, 12/417,723, 12/417,786, and12/417,904.

In any of the methods disclosed herein, radiation may be applied from adevice that is in a vault.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entirety. In case of conflict, the presentspecification, including definitions, will control. In addition, thematerials, methods, and examples are illustrative only and not intendedto be limiting.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic view of a wood processing system.

FIG. 2 is a diagrammatic view of a wood composite manufacturing system.

FIG. 3 is a diagram that illustrates changing a molecular and/or asupramolecular structure of a fibrous material.

FIG. 4 is a perspective, cut-away view of a gamma irradiator.

FIG. 5 is an enlarged perspective view of region R of FIG. 4.

FIG. 6 is a schematic diagram of a DC accelerator.

FIG. 7 is a schematic diagram of a field ionization source.

FIG. 8 is a schematic diagram of an electrostatic ion separator.

FIG. 9 is a schematic diagram of a field ionization generator.

FIG. 10 is a schematic diagram of a thermionic emission source.

FIG. 11 is a schematic diagram of a microwave discharge ion source.

FIG. 12 is a schematic diagram of a recirculating accelerator.

FIG. 13 is a schematic diagram of a static accelerator.

FIG. 14 is a schematic diagram of a dynamic linear accelerator.

FIG. 15 is a schematic diagram of a van de Graaff accelerator.

FIG. 16 is a schematic diagram of a folded tandem accelerator.

DETAILED DESCRIPTION

As discussed above, the invention is based, in part, on the discoverythat by irradiating fibrous materials, e.g., cellulosic andlignocellulosic materials, at appropriate levels, the molecularstructure of at least a cellulosic portion of the fibrous material canbe changed. For example, the change in molecular structure can include achange in any one or more of an average molecular weight, averagecrystallinity, surface area, polymerization, porosity, branching,grafting, and domain size of the cellulosic portion. These changes inmolecular structure can in turn result in favorable alterations of thephysical characteristics exhibited by the fibrous materials. Moreover,the functional groups of the fibrous material can be favorably altered.

Various cellulosic and lignocellulosic materials, their uses, andapplications have been described in U.S. Pat. Nos. 7,307,108, 7,074,918,6,448,307, 6,258,876, 6,207,729, 5,973,035 and 5,952,105; and in variouspatent applications, including “FIBROUS MATERIALS AND COMPOSITES,”PCT/US2006/010648, filed on Mar. 23, 2006, and “FIBROUS MATERIALS ANDCOMPOSITES,” U.S. Patent Application Publication No. 2007/0045456. Theaforementioned documents are all incorporated herein by reference intheir entireties. The cellulosic or lignocellulosic material caninclude, for example, paper waste, wood, particle board, sawdust,silage, grasses, rice hulls, bagasse, cotton, jute, hemp, flax, bamboo,sisal, abaca, straw, corn cobs, corn stover, switchgrass, alfalfa, hay,rice hulls, coconut hair, cotton, seaweed, algae, and mixtures thereof.In some cases, the cellulosic or lignocellulosic material includes acompressed cellulosic or lignocellulosic material, for examplecompressed grass, straw or hay. Such compressed materials can be used,for example, as building materials.

Relatively low doses of radiation can crosslink, graft, or otherwiseincrease the molecular weight of a cellulosic or lignocellulosicmaterial (e.g., cellulose). In some embodiments, the starting numberaverage molecular weight (prior to irradiation) of wood is from about200,000 to about 3,200,000, , from about 250,000 to about 1,000,000 orfrom about 250,000 to about 700,000. In some embodiments, the startingnumber average molecular weight (prior to irradiation) of wood fibers orparticles is from about 20,000 to about 1,000,000, e.g., from about25,000 to about 500,000. The number average molecular weight afterirradiation is greater than the starting number average molecularweight, for example by at least about 10%, 25%, 50%, 75%, 100%, 150%,200%, 300%, or as much as 500%. For example, if the starting numberaverage molecular weight is in the range of about 20,000 to about1,000,000, the number average molecular weight after irradiation is insome instances from about 40,000 to about 2,000,000.

As will be discussed in further detail below, the crosslinking,grafting, or otherwise increasing of the molecular weight of a naturalor synthetic cellulosic material can be performed in a controlled andpredetermined manner to provide desired properties for a particularapplication, such as strength, by selecting the type or types ofradiation employed and/or dose or doses of radiation applied.

The new methods can be used to favorably alter various properties ofwood, wood fiber, or wood fiber containing composites by applyingionizing radiation at selected times and in controlled doses. Forexample, treating pine lumber with radiation can result a relativelyhigher strength structural material.

Wood fibers having increased molecular weight can be used in makingcomposites, such as fiber-resin composites, having improved mechanicalproperties, for example abrasion resistance, compression strength,fracture resistance, impact strength, bending strength, tensile modulus,flexural modulus, and elongation at break. Crosslinking, grafting, orotherwise increasing the molecular weight of a selected material canimprove the thermal stability of the material relative to an untreatedmaterial. Increasing the thermal stability of the selected material canallow it to be processed at higher temperatures without degradation. Inaddition, treating the cellulosic material with radiation can sterilizethe material, which should reduce the tendency of the wood or compositeto promote the growth of fungus, mold, mildew, microorganisms, insects,e.g., bark beetles, nematodes, or the like.

Ionizing radiation can also be used to control the functionalization ofthe fibrous material, i.e., the functional groups that are present on orwithin the material.

Ionizing radiation can be applied to increase the molecular weight ofwood at any desired stage in a lumber manufacturing or milling process.For example, referring to FIG. 1, radiation can be applied to raw logs,sawn lumber, or after edging, trimming, or other further processing. Insome cases it may be desirable to irradiate a final product formed ofthe wood, for example a baseball bat, gunstock, article of furniture, orflooring material. Irradiation at this final stage allows the wood to bemilled or otherwise processed to a desired shape in a relatively softstate, and subsequently irradiated to increase its hardness and othermechanical properties. In other cases, it may be desirable to irradiatethe wood earlier, e.g., to increase the modulus of the wood sufficientlyto allow it to withstand further processing without breaking or beingdamaged. The wood may be irradiated before or after drying steps such askiln or air drying. It can be generally preferable that the wood be in arelatively dry state during irradiation.

After treatment with ionizing radiation, the second cellulosic and/orlignocellulosic material can be combined with a material, such as aresin, and formed into a composite, e.g., by compression molding,injection molding, or extrusion. Forming resin-fiber composites isdescribed, e.g., in WO 2006/102543. Once composites are formed, they canbe irradiated to further increase the molecular weight of thecarbohydrate-containing material while in the composite.

Alternatively, a fibrous material that includes a first cellulosicand/or lignocellulosic material having a first molecular weight can becombined with a material, such as a resin, to provide a composite, andthen the composite can be irradiated with ionizing radiation so as toprovide a second cellulosic and/or lignocellulosic material having asecond molecular weight higher than the first molecular weight. Forexample, referring to FIG. 2, radiation may be applied to raw logs;after debarking; after chipping to a desired particle of fiber size;after mixing with resin, either before or after forming steps such asextrusion, laying up or molding; after curing, or during curing toeffect or enhance curing; or during or after any further processingsteps. It is noted that the bark obtained during debarking can, ifdesired, be used to form pulp, e.g., using the methods described in myapplication filed Apr. 30, 2008, U.S. Ser. No. 61/049,391.

Advantageously, irradiation can cause bonding between the resin and thefibrous material at grafting sites, producing a synergistic effect onthe physical characteristics of the composite. This bonding can beenhanced by functionalization of the fibrous material as a result ofirradiation.

In some embodiments, the resin is a cross-linkable resin, and, as such,it crosslinks as the carbohydrate-containing material increases inmolecular weight, which can provide a synergistic effect to providemaximum mechanical properties to a composite. For example, suchcomposites can have excellent low temperature performance, e.g., havinga reduced tendency to break and/or crack at low temperatures, e.g.,temperatures below 0° C., e.g., below −10° C., −20° C., −40° C., −50°C., −60° C. or even below −100° C., and/or excellent performance at hightemperatures, e.g., capable of maintaining their advantageous mechanicalproperties at relatively high temperature, , at temperatures above 100°C., e.g., above 125° C., 150° C., 200° C., 250° C., 300° C., 400° C., oreven above 500° C. In addition, such composites can have excellentchemical resistance, e.g., resistance to swelling in a solvent, e.g., ahydrocarbon solvent, resistance to chemical attack, e.g., by strongacids, strong bases, strong oxidants (e.g., chlorine or bleach) orreducing agents (e.g., active metals such as sodium and potassium).

In some embodiments, the resin, or other matrix material, does notcrosslink during irradiation. In some embodiments, additional radiationis applied while the carbohydrate-containing material is within thematrix to further increase the molecular weight of thecarbohydrate-containing material. In some embodiments, the radiationcauses bonds to form between the matrix and the carbohydrate-containingmaterial.

In some embodiments, radiation is applied at more than one point duringthe manufacturing process. For example, a first dose of radiation may beapplied to wood fibers prior to mixing them with a resin matrix, toimprove their processability, and a second dose may be applied to thefiber/resin mixture to improve the mechanical properties of thecomposite. As another example, a first dose of radiation may be appliedto a wood starting material, such as a log or a wood beam, board orsheet, to improve its properties for further processing, and a seconddose of radiation may be applied to a product manufactured from the woodstarting material, such as a baseball bat, gunstock or piece offurniture, to improve its final properties.

Irradiating to Affect Material Functional Groups

After treatment with one or more ionizing radiations, such as photonicradiation (e.g., X-rays or gamma-rays), e-beam radiation, or irradiationwith particles heavier than electrons that are positively or negativelycharged (e.g., protons or carbon ions), any of thecarbohydrate-containing materials or mixtures described herein becomeionized; that is, they include radicals at levels that are detectable,e.g., with an electron spin resonance spectrometer. After ionization,any material that has been ionized can be quenched to reduce the levelof radicals in the ionized material, e.g., such that the radicals are nolonger detectable with the electron spin resonance spectrometer. Forexample, the radicals can be quenched by the application of a sufficientpressure to the ionized material and/or contacting the ionized materialwith a fluid, such as a gas or liquid, that reacts with (quenches) theradicals. Various gases, for example nitrogen or oxygen, or liquids, canbe used to at least aid in the quenching of the radicals and tofunctionalize the ionized material with desired functional groups. Thus,irradiation followed by quenching can be used to provide a material withdesired functional groups, including for example one or more of thefollowing: aldehyde groups, enol groups, nitroso groups, nitrile groups,nitro groups, ketone groups, amino groups, alkyl amino groups, alkylgroups, chloroalkyl groups, chlorofluoroalkyl groups, and/or carboxylicacid groups. These groups increase the hydrophilicity of the region ofthe material where they are present. In some implementations, thematerial is irradiated and quenched, before or after processing stepssuch as coating and calendaring, to affect the functionality withinand/or at the surface of the material and thereby affect properties ofthe material such as the receptivity of the material surface to paint,adhesive, coatings, and the like. In the case of composite materials,the functional groups can allow the irradiated fibrous material to bemore easily dispersed in a resin or other matrix material.

FIG. 3 illustrates changing a molecular and/or a supramolecularstructure of a fibrous material, such as wood, wood fiber or woodparticles, by pretreating the fibrous material with ionizing radiation,such as with electrons or ions of sufficient energy to ionize thematerial, to provide a first level of radicals. As shown in FIG. 3, ifthe ionized material remains in the atmosphere, it will be oxidized,e.g., to an extent that carboxylic acid groups are generated by reactingwith the atmospheric oxygen. Since the radicals can “live” for some timeafter irradiation, e.g., longer than 1 day, 5 days, 30 days, 3 months, 6months, or even longer than 1 year, material properties can continue tochange over time, which in some instances can be undesirable.

Detecting radicals in irradiated samples by electron spin resonancespectroscopy and radical lifetimes in such samples is discussed inBartolotta et al., Physics in Medicine and Biology, 46 (2001), 461-471and in Bartolotta et al., Radiation Protection Dosimetry, Vol. 84, Nos.1-4, pp. 293-296 (1999). As shown in FIG. 3, the ionized material can bequenched to functionalize and/or to stabilize the ionized material.

In some embodiments, quenching includes an application of pressure tothe ionized material, such as by mechanically deforming the material,e.g., directly mechanically compressing the material in one, two, orthree dimensions, or applying pressure to a fluid in which the materialis immersed, e.g., isostatic pressing. In such instances, thedeformation of the material itself brings radicals, which are oftentrapped in crystalline domains, in close enough proximity so that theradicals can recombine, or react with another group. In some instances,the pressure is applied together with the application of heat, such as asufficient quantity of heat to elevate the temperature of the materialto above a melting point or softening point of a component of theionized material, such as lignin, cellulose, or hemicellulose. Heat canimprove molecular mobility in the material, which can aid in thequenching of the radicals. When pressure is utilized to quench, thepressure can be greater than about 1000 psi, such as greater than about1250 psi, 1450 psi, 3625 psi, 5075 psi, 7250 psi, 10000 psi, or evengreater than 15000 psi.

In some embodiments, quenching includes contacting the ionized materialwith a fluid, such as a liquid or gas, e.g., a gas capable of reactingwith the radicals, such as acetylene or a mixture of acetylene innitrogen, ethylene, chlorinated ethylenes or chlorofluoroethylenes,propylene or mixtures of these gases. In other particular embodiments,quenching includes contacting the ionized material with a liquid, e.g.,a liquid soluble in, or at least capable of penetrating into the ionizedmaterial and reacting with the radicals, such as a diene, such as1,5-cyclooctadiene. In some specific embodiments, the quenching includescontacting the ionized material with an antioxidant, such as Vitamin E.If desired, the material can include an antioxidant dispersed therein,and the quenching can come from contacting the antioxidant dispersed inthe material with the radicals.

Other methods for quenching are possible. For example, any method forquenching radicals in polymeric materials described in Muratoglu et al.,U.S. Patent Application Publication No. 2008/0067724 and Muratoglu etal., U.S. Pat. No. 7,166,650, the disclosures of which are incorporatedby reference herein in their entireties, can be utilized for quenchingany ionized material described herein. Furthermore any quenching agent(described as a “sensitizing agent” in the above-noted Muratogludisclosures) and/or any antioxidant described in either Muratoglureference can be utilized to quench any ionized material.

Functionalization can be enhanced by utilizing heavy charged ions, suchas any of the heavier ions described herein. For example, if it isdesired to enhance oxidation, charged oxygen ions can be utilized forthe irradiation. If nitrogen functional groups are desired, nitrogenions or any ion that includes nitrogen can be utilized. Likewise, ifsulfur or phosphorus groups are desired, sulfur or phosphorus ions canbe used in the irradiation.

In some embodiments, after quenching any of the quenched ionizedmaterials described herein can be further treated with one or morefurther doses of radiation, such as ionizing or non-ionizing radiation,sonication, pyrolysis, and oxidation for additional molecular and/orsupramolecular structure change.

In some embodiments, the fibrous material is irradiated under a blanketof an inert gas, e.g., helium or argon, prior to quenching.

In some cases, the materials can be exposed to a particle beam in thepresence of one or more additional fluids (e.g., gases and/or liquids).Exposure of a material to a particle beam in the presence of one or moreadditional fluids can increase the efficiency of the treatment.

In some embodiments, the material is exposed to a particle beam in thepresence of a fluid such as air. Particles accelerated in any one ormore of the types of accelerators disclosed herein (or another type ofaccelerator) are coupled out of the accelerator via an output port(e.g., a thin membrane such as a metal foil), pass through a volume ofspace occupied by the fluid, and are then incident on the material. Inaddition to directly treating the material, some of the particlesgenerate additional chemical species by interacting with fluid particles(e.g., ions and/or radicals generated from various constituents of air,such as ozone and oxides of nitrogen). These generated chemical speciescan also interact with the material, and can act as initiators for avariety of different chemical bond-breaking reactions in the material.For example, any oxidant produced can oxidize the material, which canresult in molecular weight reduction. In certain embodiments, additionalfluids can be selectively introduced into the path of a particle beambefore the beam is incident on the material. As discussed above,reactions between the particles of the beam and the particles of theintroduced fluids can generate additional chemical species, which reactwith the material and can assist in functionalizing the material, and/orotherwise selectively altering certain properties of the material. Theone or more additional fluids can be directed into the path of the beamfrom a supply tube, for example. The direction and flow rate of thefluid(s) that is/are introduced can be selected according to a desiredexposure rate and/or direction to control the efficiency of the overalltreatment, including effects that result from both particle-basedtreatment and effects that are due to the interaction of dynamicallygenerated species from the introduced fluid with the material. Inaddition to air, exemplary fluids that can be introduced into the ionbeam include oxygen, nitrogen, one or more noble gases, one or morehalogens, and hydrogen.

The location of the functional groups can be controlled by, for example,selecting a particular type and dose of ionizing particles. For example,gamma radiation tends to affect the functionality of molecules withinthe material, while electron beam radiation tends to preferentiallyaffect the functionality of molecules at the surface.

In some cases, functionalization of the material can occursimultaneously with irradiation, rather than as a result of a separatequenching step. In this case, the type of functional groups and degreeof oxidation can be affected in various ways, for example by controllingthe gas blanketing the material to be irradiated, through which theirradiating beam passes. Suitable gases include nitrogen, oxygen, air,ozone, nitrogen dioxide, sulfur dioxide, and chlorine.

In some embodiments, functionalization results in the formation of enolgroups in the fibrous material. This can enhance the receptivity of thefunctionalized material to inks, adhesives, coatings, and the like, andcan provide grafting sites.

Cooling Irradiated Materials

During treatment of the materials discussed above with ionizingradiation, especially at high dose rates, such as at rates greater then0.15 Mrad per second, e.g., 0.25 Mrad/s, 0.35 Mrad/s, 0.5 Mrad/s, 0.75Mrad/s or even greater than 1 Mrad/sec, the materials can retainsignificant quantities of heat so that the temperature of the materialbecomes elevated. While higher temperatures can, in some embodiments, beadvantageous, e.g., when a faster reaction rate is desired, it isadvantageous to control the heating to retain control over the chemicalreactions initiated by the ionizing radiation, such as crosslinking,chain scission and/or grafting, e.g., to maintain process control.

For example, in one method, the material is irradiated at a firsttemperature with ionizing radiation, such as photons, electrons or ions(e.g., singularly or multiply charged cations or anions), for asufficient time and/or a sufficient dose to elevate the material to asecond temperature higher than the first temperature. The irradiatedmaterial is then cooled to a third temperature below the secondtemperature. If desired, the cooled material can be treated one or moretimes with radiation, e.g., with ionizing radiation. If desired, coolingcan be applied to the material after and/or during each radiationtreatment.

Cooling can in some cases include contacting the material with a fluid,such as a gas, at a temperature below the first or second temperature,such as gaseous nitrogen at or about 77 K. Even water, such as water ata temperature below nominal room temperature (e.g., 25 degrees Celsius)can be utilized in some implementations.

Types of Radiation

The radiation can be provided by, e.g., 1) heavy charged particles, suchas alpha particles, 2) electrons, produced, for example, in beta decayor electron beam accelerators, or 3) electromagnetic radiation, forexample, gamma rays, x rays, or ultraviolet rays. Different forms ofradiation ionize the biomass via particular interactions, as determinedby the energy of the radiation.

Heavy charged particles primarily ionize matter via Coulomb scattering;furthermore, these interactions produce energetic electrons that canfurther ionize matter. Alpha particles are identical to the nucleus of ahelium atom and are produced by the alpha decay of various radioactivenuclei, such as isotopes of bismuth, polonium, astatine, radon,francium, radium, several actinides, such as actinium, thorium, uranium,neptunium, curium, californium, americium, and plutonium.

Electrons interact via Coulomb scattering and bremsstrahlung radiationproduced by changes in the velocity of electrons. Electrons can beproduced by radioactive nuclei that undergo beta decay, such as isotopesof iodine, cesium, technetium, and iridium. Alternatively, an electrongun can be used as an electron source via thermionic emission.

Electromagnetic radiation interacts via three processes: photoelectricabsorption, Compton scattering, and pair production. The dominatinginteraction is determined by the energy of the incident radiation andthe atomic number of the material. The summation of interactionscontributing to the absorbed radiation in cellulosic material can beexpressed by the mass absorption coefficient.

Electromagnetic radiation is subclassified as gamma rays, x rays,ultraviolet rays, infrared rays, microwaves, or radiowaves, depending onits wavelength.

For example, gamma radiation can be employed to irradiate the materials.

Referring to FIGS. 4 and 5 (an enlarged view of region R), a gammairradiator 10 includes gamma radiation sources 408, e.g., ⁶⁰Co pellets,a working table 14 for holding the materials to be irradiated andstorage 16, e.g., made of a plurality iron plates, all of which arehoused in a concrete containment chamber (vault) 20 that includes a mazeentranceway 22 beyond a lead-lined door 26. Storage 16 includes aplurality of channels 30, e.g., sixteen or more channels, allowing thegamma radiation sources to pass through storage on their way proximatethe working table.

In operation, the sample to be irradiated is placed on a working table.The irradiator is configured to deliver the desired dose rate andmonitoring equipment is connected to an experimental block 31. Theoperator then leaves the containment chamber, passing through the mazeentranceway and through the lead-lined door. The operator mans a controlpanel 32, instructing a computer 33 to lift the radiation sources 12into working position using cylinder 36 attached to a hydraulic pump 40.

Gamma radiation has the advantage of a significant penetration depthinto a variety of materials in the sample. Sources of gamma rays includeradioactive nuclei, such as isotopes of cobalt, calcium, technicium,chromium, gallium, indium, iodine, iron, krypton, samarium, selenium,sodium, thalium, and xenon.

Sources of x rays include electron beam collision with metal targets,such as tungsten or molybdenum or alloys, or compact light sources, suchas those produced commercially by Lyncean.

Sources for ultraviolet radiation include deuterium or cadmium lamps.

Sources for infrared radiation include sapphire, zinc, or selenidewindow ceramic lamps.

Sources for microwaves include klystrons, Slevin type RF sources, oratom beam sources that employ hydrogen, oxygen, or nitrogen gases.

In some embodiments, a beam of electrons is used as the radiationsource. A beam of electrons has the advantages of high dose rates (e.g.,1, 5, or even 10 Mrad per second), high throughput, less containment,and less confinement equipment. In addition, electrons having energiesof 4-10 MeV can have a penetration depth of 5 to 30 mm or more, such as40 mm.

Electron beams can be generated, e.g., by electrostatic generators,cascade generators, transformer generators, low energy accelerators witha scanning system, low energy accelerators with a linear cathode, linearaccelerators, and pulsed accelerators. Electrons as an ionizingradiation source can be useful, e.g., for relatively thin materials,e.g., less than 0.5 inch, e.g., less than 0.4 inch, 0.3 inch, 0.2 inch,or less than 0.1 inch. In some embodiments, the energy of each electronof the electron beam is from about 0.25 MeV to about 7.5 MeV (millionelectron volts), e.g., from about 0.5 MeV to about 5.0 MeV, or fromabout 0.7 MeV to about 2.0 MeV. Electron beam irradiation devices may beprocured commercially from Ion Beam Applications, Louvain-la-Neuve,Belgium or the Titan Corporation, San Diego, Calif. Typical electronenergies can be 1, 2, 4.5, 7.5, or 10 MeV. Typical electron beamirradiation device power can be 1, 5, 10, 20, 50, 100, 250, or 500 kW.Typical doses may take values of 1, 5, 10, 20, 50, 100, or 200 kGy.

Tradeoffs in considering electron beam irradiation device powerspecifications include operating costs, capital costs, depreciation, anddevice footprint. Tradeoffs in considering exposure dose levels ofelectron beam irradiation would be energy costs and environment, safety,and health (ESH) concerns.

The electron beam irradiation device can produce either a fixed beam ora scanning beam. A scanning beam may be advantageous with large scansweep length and high scan speeds, as this would effectively replace alarge, fixed beam width. Further, available sweep widths of 0.5 m, 1 m,2 m or more are available.

In embodiments in which the irradiating is performed withelectromagnetic radiation, the electromagnetic radiation can have anenergy per photon (in electron volts) of greater than, for example, 10²eV, e.g., greater than 10³, 10⁴, 10⁵, 10⁶, or even greater than 10⁷ eV.In some embodiments, the electromagnetic radiation has energy per photonof between 10⁴ and 10⁷, e.g., between 10⁵ and 10⁶ eV. Theelectromagnetic radiation can have a frequency of, e.g., greater than10¹⁶ hz, greater than 10¹⁷ hz, 10¹⁸, 10¹⁹, 10²⁰, or even greater than10²¹ hz. In some embodiments, the electromagnetic radiation has afrequency of between 10¹⁸ and 10²² hz, e.g., between 10¹⁹ to 10²¹ hz.

One type of accelerator that can be used to accelerate ions producedusing the sources discussed above is a Dynamitron (available, forexample, from Radiation Dynamics Inc., now a unit of IBA,Louvain-la-Neuve, Belgium). A schematic diagram of a Dynamitronaccelerator 1500 is shown in FIG. 6. Accelerator 1500 includes aninjector 1510 (which includes an ion source), and an accelerating column1520 that includes a plurality of annular electrodes 1530. Injector 1510and column 1520 are housed within an enclosure 1540 that is evacuated bya vacuum pump 1600.

Injector 1510 produces a beam of ions 1580, and introduces beam 1580into accelerating column 1520. The annular electrodes 1530 aremaintained at different electric potentials, so that ions areaccelerated as they pass through gaps between the electrodes (e.g., theions are accelerated in the gaps, but not within the electrodes, wherethe electric potentials are uniform). As the ions travel from the top ofcolumn 1520 toward the bottom in FIG. 6, the average speed of the ionsincreases. The spacing between subsequent annular electrodes 1530typically increases, therefore, to accommodate the higher average ionspeed.

After the accelerated ions have traversed the length of column 1520, theaccelerated ion beam 1590 is coupled out of enclosure 1540 throughdelivery tube 1555. The length of delivery tube 1555 is selected topermit adequate shielding (e.g., concrete shielding) to be positionedadjacent to column 1520 to isolate the column. After passing throughtube 1555, ion beam 1590 passes through scan magnet 1550. Scan magnet1550, which is controlled by an external logic unit (not shown), cansweep accelerated ion beam 1590 in controlled fashion across atwo-dimensional plane oriented perpendicular to a central axis of column1520. As shown in FIG. 6, ion beam 1590 passes through window 1560(e.g., a metal foil window or screen) and then is directed to impinge onselected regions of a sample 1570 by scan magnet 1550.

In some embodiments, the electric potentials applied to electrodes 1530are static potentials generated, for example, by DC potential sources.In certain embodiments, some or all of the electric potentials appliedto electrodes 1530 are variable potentials generated by variablepotential sources. Suitable variable sources of large electricpotentials include amplified field sources such as klystrons, forexample. Accordingly, depending upon the nature of the potentialsapplied to electrodes 1530, accelerator 1500 can operate in eitherpulsed or continuous mode.

To achieve a selected accelerated ion energy at the output end of column1520, the length of column 1520 and the potentials applied to electrodes1530 are chosen based on considerations that are well-known in the art.However, it is notable that to reduce the length of column 1520,multiply-charged ions can be used in place of singly-charged ions. Thatis, the accelerating effect of a selected electric potential differencebetween two electrodes is greater for an ion bearing a charge ofmagnitude 2 or more than for an ion bearing a charge of magnitude 1.Thus, an arbitrary ion X²⁺ can be accelerated to a final energy E over ashorter length than a corresponding arbitrary ion X⁺. Triply- andquadruply-charged ions (e.g., X³⁺ and X⁴⁺) can be accelerated to finalenergy E over even shorter distances. Therefore, the length of column1520 can be significantly reduced when ion beam 1580 includes primarilymultiply-charged ion species.

To accelerate positively-charged ions, the potential differences betweenelectrodes 1530 of column 1520 are selected so that the direction ofincreasing field strength in FIG. 6 is downward (e.g., toward the bottomof column 1520). Conversely, when accelerator 1500 is used to acceleratenegatively-charged ions, the electric potential differences betweenelectrodes 1530 are reversed in column 1520, and the direction ofincreasing field strength in FIG. 6 is upward (e.g., toward the top ofcolumn 1520). Reconfiguring the electric potentials applied toelectrodes 1530 is a straightforward procedure, so that accelerator 1500can be converted relatively rapidly from accelerating positive ions toaccelerating negative ions, or vice versa. Similarly, accelerator 1500can be converted rapidly from accelerating singly-charged ions toaccelerating multiply-charged ions, and vice versa.

Doses

In some embodiments, the low dose irradiating, to increase molecularweight (with any radiation source or a combination of sources), isperformed until the material receives a dose of at least 0.1 MRad, e.g.,at least 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, or 5.0 Mrad. Insome embodiments, the irradiating is performed until the materialreceives a dose of between 0.25 Mrad and 5.0 Mrad, e.g., between 0.5Mrad and 4.0 Mrad or between 1.0 Mrad and 3.0 Mrad.

The doses discussed above are also suitable for functionalization of thematerial, with the degree of functionalization generally being higherthe higher the dose.

It can be desirable to irradiate multiple times to achieve a given finaldose, e.g., by delivering a 1 MRad dose 10 times, to provide a finaldose of 10 MRad. This may prevent overheating of the irradiatedmaterial, particularly if the material is cooled between doses.

It also can be desirable to irradiate from multiple directions,simultaneously or sequentially, in order to achieve a desired degree ofpenetration of radiation into the material. For example, depending onthe density and moisture content of the wood and the type of radiationsource used (e.g. gamma or electron beam), the maximum penetration ofradiation into the wood may be only about 0.75 inch. In such a case, athicker section (up to 1.5 inch) can be irradiated by first irradiatingthe wood from one side, and then turning the wood over and irradiatingfrom the other side. Irradiation from multiple directions can beparticularly useful with electron beam radiation, which irradiatesfaster than gamma radiation but typically does not achieve as great apenetration depth.

In some embodiments, the irradiating is performed at a dose rate ofbetween 5.0 and 1500.0 kilorads/hour, e.g., between 10.0 and 750.0kilorads/hour or between 50.0 and 350.0 kilorads/hours. When highthroughput is desired, radiation can be applied at, e.g., 0.5 to 3.0MRad/sec, or even faster, using cooling to avoid overheating theirradiated material.

In some embodiments in which a composite is irradiated, the resin matrixincludes a resin that is cross-linkable and as such it crosslinks as thecarbohydrate-containing material increases in molecular weight, whichcan provide a synergistic effect to optimize the physical properties ofthe composite. In these embodiments, the dose of radiation is selectedto be sufficiently high so as to increase the molecular weight of thecellulosic fibers, i.e., at least about 0.1 MRad, while beingsufficiently low so as to avoid deleteriously affecting the resinmatrix. The upper limit on the dose will vary depending on thecomposition of the resin matrix, but in some embodiments the preferreddose is less than about 10 MRad.

In some embodiments, two or more radiation sources are used, such as twoor more ionizing radiations. For example, samples can be treated, in anyorder, with a beam of electrons, followed by gamma radiation and UVlight having wavelengths from about 100 nm to about 280 nm. In someembodiments, samples are treated with three ionizing radiation sources,such as a beam of electrons, gamma radiation, and energetic UV light.

Irradiating Wood

The methods described herein may be used on any desired type of wood.The wood can be irradiated in its initial form, i.e., as a log, or canbe irradiated at any subsequent stage of processing. Preferably, thewood has a relatively low moisture content, for example a moisturecontent of less than 25%, e.g., less than 20%. In some cases, forexample when the wood has been dried, the moisture content will be fromabout 6% to about 18%. In some implementations, the weight percent watercontent (moisture content) may be less than 5%, 4%, 3%, 2%, 1% or evenless than 0.5%. The moisture content may, in some implementations, bewithin the ranges of 1% to 8%, e.g., 2% to 6%. A relatively low moisturecontent will allow penetration of the wood by ionizing radiation, andmay enhance the stability of radicals formed within the wood by theradiation.

Generally the wood has a density of less than 1.4 g/cm³, e.g., about 1.0to 1.2 g/cm³.

Composite Materials

The term “wood composite,” as used herein, refers to a material thatincludes wood chips, wood fibers, wood particles, or wood flourdispersed in a resin matrix. Such composites include, for example,particleboard, chipboard, oriented strand board (OSB), waferboard,Sterling board, and fiberboard.

Particleboard is often formed from low quality logs and residue fromwood products manufacturing. For example, fast growing species such asaspen and poplar can be used in the form of whole-tree chipped furnish(wood particles). In some implementations, chips are reduced intoparticles by using a hammermill, disk-refiner, or flaker, after whichthe particles are dried to a low moisture content, e.g., about 3 to 5%.If desired, the dried furnish may be classified into predeterminedparticle sizes such as fine and coarse using different mesh sizescreens. The furnish (or a portion of the furnish having a desiredparticle size) is then blended with a resin matrix or binder. Theconcentration of the binder in the finished product is generallyrelatively low, for example from about 5 to 20%, typically about 5 to10%, e.g., about 1 to 5%. In some cases, the furnish/resin blend isformed into a mat prior to curing. If desired, a blend of resin with afine particle size furnish can be used to form an outer layer on the topand bottom of a core layer that is formed of a blend of resin with acoarse particle size furnish. The mat is then cured, e.g., under heatand pressure, to form a finished particleboard panel.

Oriented strand board (OSB) and the like are also engineered woodproducts that are formed by layering strands or chips of wood or otherfibers in specific orientations. These boards are typically manufacturedin mats of cross-oriented layers of thin, rectangular wood or otherfiber strips compressed and bonded together with wax and resin adhesives(e.g., about 95% wood/fiber and about 5% wax/resin). The layers arecreated by shredding the wood/fiber into strips, which are sifted andthen oriented, e.g., on a conveyor belt. Alternating layers are added tocreate the final product, which is placed in a thermal press to compressthe materials and bond them by heat activation and curing of the resin.Individual panels can then be cut from the mats into finished sizes.

Irradiation can be performed at any desired stage (or at several stages)in these processes. For example, logs or chips can be irradiated priorto the formation of the furnish, strands, or chips, or the furnish canbe irradiated prior to blending with the resin/wax. In some cases, theblend of resin and furnish is irradiated, in which case irradiation mayassist with cross-linking of the resin. If a radiation cross-linkableresin is utilized, heat curing and/or pressure densification of theparticleboard or OSB may not be necessary. Irradiation can also beperformed on the finished, cured particleboard or OSB. If desired,irradiation can be performed at more than one stage of the process, forexample on the furnish and then on the cured particleboard.

The process for forming fiberboard is similar to that for formingparticleboard and OSB, except that wood fibers are used instead of therelatively larger particles used in the furnish described above. Chipsmay be converted to fibers using various techniques, including forexample rotary shearers, single or double disk refiners, defibrators,pressurized refiners and atmospheric refiners. The resulting fiber isblended with resin and cured, as discussed above with regard toparticleboard. As discussed above, irradiation can be performed at anydesired stage of the process, from irradiation of the logs from whichthe fiber will be formed to irradiation of the cured board.

In either of these processes, the resin can be any thermoplastic,thermoset, elastomer, adhesive, or mixtures of these resins. Suitableresins include epoxies, urea formaldehydes, melamines, phenolic resinsand urethanes.

Other composites are formed by, e.g., extruding, injection molding,compression molding, rotomolding, blow molding, or casting, a mixture ofwood chips, particles or fibers and a resin binder or matrix. In thistype of composite, the concentration of resin is generally higher, e.g.,from about 40% to about 80% resin. Such composites may be irradiated inthe same manner discussed above for particleboard and fiber board.

In some embodiments, the particles or fibers are randomly orientedwithin the matrix. In other embodiments, the fibers can be substantiallyoriented, such as in one, two, three or four directions. If desired, thefibers can be continuous or discrete. The particles or fibers may have ahigh aspect ratio (L/D). For example, the average length-to-diameterratio of the fibrous material can be greater than 8/1, e.g., greaterthan 10/1, greater than 15/1, greater than 20/1, greater than 25/1, orgreater than 50/1. An average length of the fibrous material can be,e.g., between about 0.5 mm and 2.5 mm, e.g., between about 0.75 mm and1.0 mm, and an average width (i.e., diameter) of the fibrous materialcan be, e.g., between about 5 μm and 50 μm, e.g., between about 10 μmand 30 μm.

In some implementations, the particleboard, OSB, or fiberboard is usedas an intermediate product to form a laminate, e.g., a high pressurelaminate (HPL), or a veneer. In this case, an overlay material such aspaper, foil, melamine impregnated paper or a polymer film is laminatedto one or both broad surfaces of the board. Irradiation can be performedbefore, during and/or after the lamination step. In some cases,irradiation may also improve the mechanical properties of the overlay,for example if the overlay includes paper, and thus it may be desirableto perform an irradiating step during or after lamination.

In any of the processes described above, other types of fibrous materialmay be used in place of wood chips or particles, e.g., fibrous materialderived from other cellulosic sources.

Ion Generation

Various methods may be used for the generation of ions suitable for ionbeams which may be used in treating the cellulosic or lignocellulosicmaterials. After the ions have been generated, they are typicallyaccelerated in one or more of various types of accelerators, and thendirected to impinge on the cellulosic or lignocellulosic materials.

(i) Hydrogen Ions

Hydrogen ions can be generated using a variety of different methods inan ion source. Typically, hydrogen ions are introduced into an ionizingchamber of an ion source, and ions are produced by supplying energy togas molecules. During operation, such chambers can produce large ioncurrents suitable for seeding a downstream ion accelerator.

In some embodiments, hydrogen ions are produced via field ionization ofhydrogen gas. A schematic diagram of a field ionization source is shownin FIG. 7. Field ionization source 1100 includes a chamber 1170 whereionization of gas molecules (e.g., hydrogen gas molecules) occurs. Gasmolecules 1150 enter chamber 1170 by flowing along direction 1155 insupply tube 1120. Field ionization source 1100 includes an ionizationelectrode 1110. During operation, a large potential V_(E) (relative to acommon system ground potential) is applied to electrode 1110. Molecules1150 that circulate within a region adjacent to electrode 1110 areionized by the electric field that results from potential V_(E). Alsoduring operation, an extraction potential V_(X) is applied to extractors1130. The newly-formed ions migrate towards extractors 1130 under theinfluence of the electric fields of potentials V_(E) and V_(X). Ineffect, the newly-formed ions experience repulsive forces relative toionization electrode 1110, and attractive forces relative to extractors1130. As a result, certain of the newly-formed ions enter discharge tube1140, and propagate along direction 1165 under the influence ofpotentials V_(E) and V_(X).

Depending upon the sign of potential V_(E) (relative to the commonground potential), both positively and negatively charged ions can beformed. For example, in some embodiments, a positive potential can beapplied to electrode 1110 and a negative potential can be applied toextractors 1130. Positively charged hydrogen ions (e.g., protons H⁺)that are generated in chamber 1170 are repelled away from electrode 1110and toward extractors 1130. As a result, discharged particle stream 1160includes positively charged hydrogen ions that are transported to aninjector system.

In certain embodiments, a negative potential can be applied to electrode1110 and a positive potential can be applied to extractors 1130.Negatively charged hydrogen ions (e.g., hydride ions H⁻) that aregenerated in chamber 1170 are repelled away from electrode 1110 andtoward extractors 1130. Discharged particle stream 1160 includesnegatively charged hydrogen ions, which are then transported to aninjector system.

In some embodiments, both positive and negative hydrogen ions can beproduced via direct thermal heating of hydrogen gas. For example,hydrogen gas can be directed to enter a heating chamber that isevacuated to remove residual oxygen and other gases. The hydrogen gascan then be heated via a heating element to produce ionic species.Suitable heating elements include, for example, arc dischargeelectrodes, heating filaments, heating coils, and a variety of otherthermal transfer elements.

In certain embodiments, when hydrogen ions are produced via either fieldemission or thermal heating, various hydrogen ion species can beproduced, including both positively and negatively charged ion species,and singly- and multiply-charged ion species. The various ion speciescan be separated from one another via one or more electrostatic and/ormagnetic separators. FIG. 8 shows a schematic diagram of anelectrostatic separator 1175 that is configured to separate a pluralityof hydrogen ion species from one another. Electrostatic separator 1175includes a pair of parallel electrodes 1180 to which a potential V_(S)is applied by a voltage source (not shown). Particle stream 1160,propagating in the direction indicated by the arrow, includes a varietyof positively- and negatively-charged, and singly- and multiply-charged,ion species. As the various ion species pass through electrodes 1180,the electric field between the electrodes deflects the ion trajectoriesaccording to the magnitude and sign of the ion species. In FIG. 8, forexample, the electric field points from the lower electrode toward theupper electrode in the region between electrodes 1180. As a result,positively-charged ions are deflected along an upward trajectory in FIG.8, and negatively-charged ions are deflected along a downwardtrajectory. Ion beams 1162 and 1164 each correspond topositively-charged ion species, with the ion species in ion beam 1162having a larger positive charge than the ion species is beam 1164 (E.G.,due to the larger positive charge of the ions in beam 1162, the beam isdeflected to a greater extent). Similarly, ion beams 1166 and 1168 eachcorrespond to negatively-charged ion species, with the ion species inion beam 1168 having a larger negative charge than the ion species inion beam 1166 (and thereby being deflected to a larger extent by theelectric field between electrodes 1180). Beam 1169 includes neutralparticles originally present in particle stream 1160; the neutralparticles are largely unaffected by the electric field betweenelectrodes 1180, and therefore pass undeflected through the electrodes.

Each of the separated particle streams enters one of delivery tubes1192, 1194, 1196, 1198, and 1199, and can be delivered to an injectorsystem for subsequent acceleration of the particles, or steered to beincident directly on the cellulosic or lignocellulosic material.Alternatively, or in addition, any or all of the separated particlestreams can be blocked to prevent ion and/or atomic species fromreaching cellulosic or lignocellulosic material. As yet anotheralternative, certain particle streams can be combined and then directedto an injector system and/or steered to be incident directly on thecellulosic or lignocellulosic material using known techniques.

In general, particle beam separators can also use magnetic fields inaddition to, or rather than, electric fields for deflecting chargedparticles. In some embodiments, particle beam separators includemultiple pairs of electrodes, where each pair of electrodes generates anelectric field that deflects particles passing therethrough.Alternatively, or in addition, particle beam separators can include oneor more magnetic deflectors that are configured to deflect chargedparticles according to magnitude and sign of the particle charges.

(ii) Noble Gas Ions

Noble gas atoms (e.g., helium atoms, neon atoms, argon atoms) formpositively-charged ions when acted upon by relatively strong electricfields. Methods for generating noble gas ions therefore typicallyinclude generating a high-intensity electric field, and then introducingnoble gas atoms into the field region to cause field ionization of thegas atoms. A schematic diagram of a field ionization generator for noblegas ions (and also for other types of ions) is shown in FIG. 9. Fieldionization generator 1200 includes a tapered electrode 1220 positionedwithin a chamber 1210. A vacuum pump 1250 is in fluid communication withthe interior of chamber 1210 via inlet 1240, and reduces the pressure ofbackground gases within chamber 1210 during operation. One or more noblegas atoms 1280 are admitted to chamber 1210 via inlet tube 1230.

During operation, a relatively high positive potential V_(T) (e.g.,positive relative to a common external ground) is applied to taperedelectrode 1220. Noble gas atoms 1280 that enter a region of spacesurrounding the tip of electrode 1220 are ionized by the strong electricfield extending from the tip; the gas atoms lose an electron to the tip,and form positively charged noble gas ions.

The positively charged noble gas ions are accelerated away from the tip,and a certain fraction of the gas ions 1290 pass through extractor 1260and exit chamber 1210, into an ion optical column that includes lens1270, which further deflects and/or focuses the ions.

Electrode 1220 is tapered to increase the magnitude of the localelectric field in the region near the apex of the tip. Depending uponthe sharpness of the taper and the magnitude of potential V_(T), theregion of space in chamber 1210 within which ionization of noble gasatoms occurs can be relatively tightly controlled. As a result, arelatively well collimated beam of noble gas ions 1290 can be obtainedfollowing extractor 1260.

As discussed above in connection with hydrogen ions, the resulting beamof noble gas ions 1290 can be transported through a charged particleoptical column that includes various particle optical elements fordeflecting and/or focusing the noble gas ion beam. The noble gas ionbeam can also pass through an electrostatic and/or magnetic separator,as discussed above in connection with FIG. 8.

Noble gas ions that can be produced in field ionization generator 1200include helium ions, neon ions, argon ions, and krypton ions. Inaddition, field ionization generator 1200 can be used to generate ionsof other gaseous chemical species, including hydrogen, nitrogen, andoxygen.

Noble gas ions may have particular advantages relative to other ionspecies when treating cellulosic or lignocellulosic material. Forexample, while noble gas ions can react with cellulosic orlignocellulosic materials, neutralized noble gas ions (e.g., noble gasatoms) that are produced from such reactions are generally inert, and donot further react with the cellulosic or lignocellulosic material.Moreover, neutral noble gas atoms do not remain embedded in thecellulosic or lignocellulosic material, but instead diffuse out of thematerial. Noble gases are non-toxic and can be used in large quantitieswithout adverse consequences to either human health or the environment.

(iii) Carbon, Oxygen, and Nitrogen Ions

Ions of carbon, oxygen, and nitrogen can typically be produced by fieldionization in a system such as field ionization source 1100 or fieldionization generator 1200. For example, oxygen gas molecules and/oroxygen atoms (e.g., produced by heating oxygen gas) can be introducedinto a chamber, where the oxygen molecules and/or atoms are fieldionized to produce oxygen ions. Depending upon the sign of the potentialapplied to the field ionization electrode, positively- and/ornegatively-charged oxygen ions can be produced. The desired ion speciescan be preferentially selected from among various ion species andneutral atoms and molecules by an electrostatic and/or magnetic particleselector, as shown in FIG. 8.

As another example, nitrogen gas molecules can be introduced into thechamber of either field ionization source 1100 or field ionizationgenerator 1200, and ionized to form positively- and/ornegatively-charged nitrogen ions by the relatively strong electric fieldwithin the chamber. The desired ion species can then be separated fromother ionic and neutral species via an electrostatic and/or magneticseparator, as shown in FIG. 8.

To form carbon ions, carbon atoms can be supplied to the chamber ofeither field ionization source 1100 or field ionization generator 1200,wherein the carbon atoms can be ionized to form either positively-and/or negatively-charged carbon ions. The desired ion species can thenbe separated from other ionic and neutral species via an electrostaticand/or magnetic separator, as shown in FIG. 8. The carbon atoms that aresupplied to the chamber of either field ionization source 1100 or fieldionization generator 1200 can be produced by heating a carbon-basedtarget (e.g., a graphite target) to cause thermal emission of carbonatoms from the target. The target can be placed in relatively closeproximity to the chamber, so that emitted carbon atoms enter the chamberdirectly following emission.

(iv) Heavier Ions

Ions of heavier atoms such as sodium and iron can be produced via anumber of methods. For example, in some embodiments, heavy ions such assodium and/or iron ions are produced via thermionic emission from atarget material that includes sodium and/or iron, respectively. Suitabletarget materials include materials such as sodium silicates and/or ironsilicates. The target materials typically include other inert materialssuch as beta-alumina. Some target materials are zeolite materials, andinclude channels formed therein to permit escape of ions from the targetmaterial.

FIG. 10 shows a thermionic emission source 1300 that includes a heatingelement 1310 that contacts a target material 1330, both of which arepositioned inside an evacuated chamber 1305. Heating element 1310 iscontrolled by controller 1320, which regulates the temperature ofheating element 1310 to control the ion current generated from targetmaterial 1330. When sufficient heat is supplied to target material 1330,thermionic emission from the target material generates a stream of ions1340. Ions 1340 can include positively-charged ions of materials such assodium, iron, and other relatively heavy atomic species (e.g., othermetal ions). Ions 1340 can then be collimated, focused, and/or otherwisedeflected by electrostatic and/or magnetic electrodes 1350, which canalso deliver ions 1340 to an injector.

Thermionic emission to form ions of relatively heavy atomic species isalso discussed, for example, in U.S. Pat. No. 4,928,033, entitled“Thermionic Ionization Source,” the entire contents of which areincorporated herein by reference.

In certain embodiments, relatively heavy ions such as sodium ions and/oriron ions can be produced by microwave discharge. FIG. 11 shows aschematic diagram of a microwave discharge source 1400 that producesions from relatively heavy atoms such as sodium and iron. Dischargesource 1400 includes a microwave field generator 1410, a waveguide tube1420, a field concentrator 1430, and an ionization chamber 1490. Duringoperation, field generator 1410 produces a microwave field whichpropagates through waveguide 1420 and concentrator 1430; concentrator1430 increases the field strength by spatially confining the field, asshown in FIG. 11. The microwave field enters ionization chamber 1490. Ina first region inside chamber 1490, a solenoid 1470 produces a strongmagnetic field 1480 in a region of space that also includes themicrowave field. Source 1440 delivers atoms 1450 to this region ofspace. The concentrated microwave field ionizes atoms 1450, and themagnetic field 1480 generated by solenoid 1470 confines the ionizedatoms to form a localized plasma. A portion of the plasma exits chamber1490 as ions 1460. Ions 1460 can then be deflected and/or focused by oneor more electrostatic and/or magnetic elements, and delivered to aninjector.

Atoms 1450 of materials such as sodium and/or iron can be generated bythermal emission from a target material, for example. Suitable targetmaterials include materials such as silicates and other stable salts,including zeolite-based materials. Suitable target materials can alsoinclude metals (e.g., iron), which can be coated on an inert basematerial such as a glass material.

Microwave discharge sources are also discussed, for example, in thefollowing U.S. Patents: U.S. Pat. No. 4,409,520, entitled “MicrowaveDischarge Ion Source,” and U.S. Pat. No. 6,396,211, entitled “MicrowaveDischarge Type Electrostatic Accelerator Having Upstream and DownstreamAcceleration Electrodes.” The entire contents of each of the foregoingpatents are incorporated herein by reference.

Particle Beam Sources

Particle beam sources that generate beams for use in irradiatingcellulosic or lignocellulosic material typically include three componentgroups: an injector, which generates or receives ions and introduces theions into an accelerator; an accelerator, which receives ions from theinjector and increases the kinetic energy of the ions; and outputcoupling elements, which manipulate the beam of accelerated ions.

(i) Injectors

Injectors can include, for example, any of the ion sources discussed inthe preceding sections above, which supply a stream of ions forsubsequent acceleration. Injectors can also include various types ofelectrostatic and/or magnetic particle optical elements, includinglenses, deflectors, collimators, filters, and other such elements. Theseelements can be used to condition the ion beam prior to entering theaccelerator; that is, these elements can be used to control thepropagation characteristics of the ions that enter the accelerator.Injectors can also include pre-accelerating electrostatic and/ormagnetic elements that accelerate charged particles to a selected energythreshold prior to entering the accelerator. An example of an injectoris shown in Iwata, Y. et al..

(ii) Accelerators

One type of accelerator that can be used to accelerate ions producedusing the sources discussed above is a Dynamitron® (available, forexample, from Radiation Dynamics Inc., now a unit of IBA,Louvain-la-Neuve, Belgium). A schematic diagram of a Dynamitron®accelerator 1500 is shown in FIG. 6 and discussed above.

Another type of accelerator that can be used to accelerate ions fortreatment of cellulosic or lignocellulosic-based material is aRhodotron® accelerator (available, for example, from IBA,Louvain-la-Neuve, Belgium). In general, Rhodotron-type acceleratorsinclude a single recirculating cavity through which ions that are beingaccelerated make multiple passes. As a result, Rhodotron® acceleratorscan be operated in continuous mode at relatively high continuous ioncurrents.

FIG. 12 shows a schematic diagram of a Rhodotron® accelerator 1700.Accelerator 1700 includes an injector 1710, which introduces acceleratedions into recirculating cavity 1720. An electric field source 1730 ispositioned within an inner chamber 1740 of cavity 1720, and generates anoscillating radial electric field. The oscillation frequency of theradial field is selected to match the transit time of injected ionsacross one pass of recirculating cavity 1720. For example, apositively-charged ion is injected into cavity 1720 by injector 1710when the radial electric field in the cavity has zero amplitude. As theion propagates toward chamber 1740, the amplitude of the radial field inchamber 1740 increases to a maximum value, and then decreases again. Theradial field points inward toward chamber 1740, and the ion isaccelerated by the radial field. The ion passes through a hole in thewall of inner chamber 1740, crosses the geometrical center of cavity1720, and passes out through another hole in the wall of inner chamber1740. When the ion is positioned at the enter of cavity 1720, theelectric field amplitude inside cavity 1720 has been reduced to zero (ornearly zero). As the ion emerges from inner chamber 1740, the electricfield amplitude in cavity 1720 begins to increase again, but the fieldis now oriented radially outward. The field magnitude during the secondhalf of the ion's pass through cavity 1720 again reaches a maximum andthen begins to diminish. As a result, the positive ion is againaccelerated by the electric field as the ion completes the second halfof a first pass through cavity 1720.

Upon reaching the wall of cavity 1720, the magnitude of the electricfield in cavity 1720 is zero (or nearly zero) and the ion passes throughan aperture in the wall and encounters one of beam deflection magnets1750. The beam deflection magnets essentially reverse the trajectory ofthe ion, as shown in FIG. 12, directing the ion to re-enter cavity 1720through another aperture in the wall of the chamber. When the ionre-enters cavity 1720, the electric field therein begins to increase inamplitude again, but is now once more oriented radially inward. Thesecond and subsequent passes of the ion through cavity 1720 follow asimilar pattern, so that the orientation of the electric field alwaysmatches the direction of motion of the ion, and the ion is acceleratedon every pass (and every half-pass) through cavity 1720.

As shown in FIG. 12, after six passes through cavity 1720, theaccelerated ion is coupled out of cavity 1720 as a portion ofaccelerated ion beam 1760. The accelerated ion beam passes through oneor more electrostatic and/or magnetic particle optical elements 1770,which can include lenses, collimators, beam deflectors, filters, andother optical elements. For example, under control of an external logicunit, elements 1770 can include an electrostatic and/or magneticdeflector that sweeps accelerated beam 1760 across a two-dimensionalplanar region oriented perpendicular to the direction of propagation ofbeam 1760.

Ions that are injected into cavity 1720 are accelerated on each passthrough cavity 1720. In general, therefore, to obtain accelerated beamshaving different average ion energies, accelerator 1700 can include morethan one output coupling. For example, in some embodiments, one or moreof deflection magnets 1750 can be modified to allow a portion of theions reaching the magnets to be coupled out of accelerator 1700, and aportion of the ions to be returned to chamber 1720. Multiple acceleratedoutput beams can therefore be obtained from accelerator 1700, each beamcorresponding to an average ion energy that is related to the number ofpasses through cavity 1720 for the ions in the beam.

Accelerator 1700 includes 5 deflection magnets 1750, and ions injectedinto cavity 1720 make 6 passes through the cavity. In general, however,accelerator 1700 can include any number of deflection magnets, and ionsinjected into cavity 1720 can make any corresponding number of passesthrough the cavity. For example, in some embodiments, accelerator 1700can include at least 6 deflection magnets and ions can make at least 7passes through the cavity (e.g., at least 7 deflection magnets and 8passes through the cavity, at least 8 deflection magnets and 9 passesthrough the cavity, at least 9 deflection magnets and 10 passes throughthe cavity, at least 10 deflection magnets and 11 passes through thecavity).

Typically, the electric field generated by field source 1730 provides asingle-cavity-pass gain of about 1 MeV to an injected ion. In general,however, higher single-pass gains are possible by providing ahigher-amplitude electric field within cavity 1720. In some embodiments,for example, the single-cavity-pass gain is about 1.2 MeV or more (e.g.,1.3 MeV or more, 1.4 MeV or more, 1.5 MeV or more, 1.6 MeV or more, 1.8MeV or more, 2.0 MeV or more, 2.5 MeV or more).

The single-cavity-pass gain also depends upon the magnitude of thecharge carried by the injected ion. For example, ions bearing multiplecharges will experience higher single-pass-cavity gain than ions bearingsingle charges, for the same electric field within cavity. As a result,the single-pass-cavity gain of accelerator 1700 can be further increasedby injecting ions having multiple charges.

In the foregoing description of accelerator 1700, a positively-chargedion was injected into cavity 1720. Accelerator 1700 can also acceleratenegatively charged ions. To do so, the negatively charged ions areinjected so that the direction of their trajectories is out of phasewith the radial electric field direction. That is, the negativelycharged ions are injected so that on each half pass through cavity 1720,the direction of the trajectory of each ion is opposite to the directionof the radial electric field. Achieving this involves simply adjustingthe time at which negatively-charged ions are injected into cavity 1720.Accordingly, accelerator 1700 is capable of simultaneously acceleratingions having the same approximate mass, but opposite charges. Moregenerally, accelerator 1700 is capable of simultaneously acceleratingdifferent types of both positively- and negatively-charged (and bothsingly- and multiply-charged) ions, provided that the transit times ofthe ions across cavity 1720 are relatively similar. In some embodiments,accelerator 1700 can include multiple output couplings, providingdifferent types of accelerated ion beams having similar or differentenergies.

Other types of accelerators can also be used to accelerate ions forirradiation of cellulosic or lignocellulosic material. For example, insome embodiments, ions can be accelerated to relatively high averageenergies in cyclotron- and/or synchrotron-based accelerators. Theconstruction and operation of such accelerators is well-known in theart. As another example, in some embodiments, Penning-type ion sourcescan be used to generate and/or accelerate ions for treating cellulosicor lignocellulosic-based material. The design of Penning-type sources isdiscussed in section 7.2.1 of Prelec (1997).

Static and/or dynamic accelerators of various types can also generallybe used to accelerate ions. Static accelerators typically include aplurality of electrostatic lenses that are maintained at different DCvoltages. By selecting appropriate values of the voltages applied toeach of the lens elements, ions introduced into the accelerator can beaccelerated to a selected final energy. FIG. 13 shows a simplifiedschematic diagram of a static accelerator 1800 that is configured toaccelerate ions to treat cellulosic or lignocellulosic material 1835.Accelerator 1800 includes an ion source 1810 that produces ions andintroduces the ions into an ion column 1820. Ion column 1820 includes aplurality of electrostatic lenses 1825 that accelerate the ionsgenerated by ion source 1810 to produce an ion beam 1815. DC voltagesare applied to lenses 1825; the potentials of the lenses remainapproximately constant during operation. Generally, the electricalpotential within each lens is constant, and the ions of ion beam 1815are accelerated in the gaps between the various lenses 1825. Ion column1820 also includes a deflection lens 1830 and a collimation lens 1832.These two lenses operate to direct ion beam 1815 to a selected positionon cellulosic or lignocellulosic material 1835, and to focus ion beam1815 onto the cellulosic or lignocellulosic material.

Although FIG. 13 shows a particular embodiment of a static accelerator,many other variations are possible and suitable for treating cellulosicor lignocellulosic material. In some embodiments, for example, therelative positions of deflection lens 1830 and collimation lens 1832along ion column 1820 can be exchanged. Additional electrostatic lensescan also be present in ion column 1820, and ion column 1820 can furtherinclude magnetostatic optical elements. In certain embodiments, a widevariety of additional elements can be present in ion column 1820,including deflectors (e.g., quadrupole, hexapole, and/or octopoledeflectors), filtering elements such as apertures to remove undesiredspecies (e.g., neutrals and/or certain ionic species) from ion beam1815, extractors (e.g., to establish a spatial profile for ion beam1815), and other electrostatic and/or magnetostatic elements.

Dynamic linear accelerators—often referred to as LINACs—can also be usedto generate an ion beam that can be used to treat cellulosic orlignocellulosic material. Typically, dynamic linear accelerators includean ion column with a linear series of radiofrequency cavities, each ofwhich produces an intense, oscillating radiofrequency (RF) field that istimed to coincide with injection and propagation of ions into the ioncolumn. As an example, devices such as klystrons can be used togenerated the RF fields in the cavities. By matching the fieldoscillations to the injection times of ions, the RF cavities canaccelerate ions to high energies without having to maintain peakpotentials for long periods of time. As a result, LINACs typically donot have the same shielding requirements as DC accelerators, and aretypically shorter in length. LINACs typically operate at frequencies of3 GHz (S-band, typically limited to relatively low power) and 1 GHz(L-band, capable of significantly higher power operation). TypicalLINACs have an overall length of 2-4 meters.

A schematic diagram of a dynamic linear accelerator 1850 (e.g., a LINAC)is shown in FIG. 14. LINAC 1850 includes an ion source 1810 and an ioncolumn 1855 that includes three acceleration cavities 1860, a deflector1865, and a focusing lens 1870. Deflector 1865 and focusing lens 1870function to steer and focus ion beam 1815 onto cellulosic orlignocellulosic material 1835 following acceleration, as discussedabove. Acceleration cavities 1860 are formed of a conductive materialsuch as copper, and function as a waveguide for the accelerated ions.Klystrons 1862, connected to each of cavities 1860, generate the dynamicRF fields that accelerate the ions within the cavities. Klystrons 1862are individually configured to produce RF fields that, together,accelerate the ions in ion beam 1815 to a final, selected energy priorto being incident on cellulosic or lignocellulosic material 1835.

As discussed above in connection with static accelerators, manyvariations of dynamic accelerator 1850 are possible and can be used toproduce an ion beam for treating cellulosic or lignocellulosic material.For example, in some embodiments, additional electrostatic lenses canalso be present in ion column 1855, and ion column 1855 can furtherinclude magnetostatic optical elements. In certain embodiments, a widevariety of additional elements can be present in ion column 1855,including deflectors (e.g., quadrupole, hexapole, and/or octopoledeflectors), filtering elements such as apertures to remove undesiredspecies (e.g., neutrals and/or certain ionic species) from ion beam1815, extractors (e.g., to establish a spatial profile for ion beam1815), and other electrostatic and/or magnetostatic elements. Inaddition to the specific static and dynamic accelerators discussedabove, other suitable accelerator systems include, for example: DCinsulated core transformer (ICT) type systems, available from NissinHigh Voltage, Japan; S-band LINACS, available from L3-PSD (USA), LinacSystems (France), Mevex (Canada), and Mitsubishi Heavy Industries(Japan); L-band LINACS, available from Iotron Industries (Canada); andILU-based accelerators, available from Budker Laboratories (Russia).

In some embodiments, van de Graaff-based accelerators can be used toproduce and/or accelerate ions for subsequent treatment of cellulosic orlignocellulosic material. FIG. 15 shows an embodiment of a van de Graaffaccelerator 1900 that includes a spherical shell electrode 1902 and aninsulating belt 1906 that recirculates between electrode 1902 and a base1904 of accelerator 1900. During operation, insulating belt 1906 travelsover pulleys 1910 and 1908 in the direction shown by arrow 1918, andcarries charge into electrode 1902. Charge is removed from belt 1906 andtransferred to electrode 1902, so that the magnitude of the electricalpotential on electrode 1902 increases until electrode 1902 is dischargedby a spark (or, alternatively, until the charging current is balanced bya load current).

Pulley 1910 is grounded, as shown in FIG. 15. A corona discharge ismaintained between a series of points or a fine wire on one side of belt1906. Wire 1914 is configured to maintain the corona discharge inaccelerator 1900. Wire 1914 is maintained at a positive potential, sothat belt 1906 intercepts positive ions moving from wire 1914 to pulley1910. As belt 1906 moves in the direction of arrow 1918, the interceptedcharges are carried into electrode 1902, where they are removed frombelt 1906 by a needle point 1916 and transferred to electrode 1902. As aresult, positive charges accumulate on the surface of electrode 1902;these charges can be discharged from the surface of electrode 1902 andused to treat cellulosic or lignocellulosic material. In someembodiments, accelerator 1900 can be configured to provide negativelycharged ions by operating wire 1914 and needle point 1916 at a negativepotential with respect to grounded pulley 1910.

In general, accelerator 1900 can be configured to provide a wide varietyof different types of positive and negative charges for treatingcellulosic or lignocellulosic material. Exemplary types of chargesinclude electrons, protons, hydrogen ions, carbon ions, oxygen ions,halogen ions, metal ions, and other types of ions.

In certain embodiments, tandem accelerators (including folded tandemaccelerators) can be used to generate ion beams for treatment ofcellulosic or lignocellulosic material. An example of a folded tandemaccelerator 1950 is shown in FIG. 16. Accelerator 1950 includes anaccelerating column 1954, a charge stripper 1956, a beam deflector 1958,and an ion source 1952.

During operation, ion source 1952 produces a beam 1960 of negativelycharged ions, which is directed to enter accelerator 1950 through inputport 1964. In general, ion source 1952 can be any type of ion sourcethat produces negatively charged ions. For example, suitable ion sourcesinclude a source of negative ions by cesium sputtering (SNICS) source, aRF-charge exchange ion source, or a toroidal volume ion source (TORVIS).Each of the foregoing exemplary ion sources is available, for example,from National Electrostatics Corporation (Middleton, Wis.).

Once inside accelerator 1950, the negative ions in beam 1960 areaccelerated by accelerating column 1954. Typically, accelerating column1954 includes a plurality of accelerating elements such as electrostaticlenses. The potential difference applied in column 1954 to acceleratethe negative ions can be generated using various types of devices. Forexample, in some embodiments, (e.g., Pelletron® accelerators), thepotential is generated using a Pelletron® charging device. Pelletron®devices include a charge-carrying belt that is formed from a pluralityof metal (e.g., steel) chain links or pellets that are bridged byinsulating connectors (e.g., formed from a material such as nylon).During operation, the belt recirculates between a pair of pulleys, oneof which is maintained at ground potential. As the belt moves betweenthe grounded pulley and the opposite pulley (e.g., the terminal pulley),the metal pellets are positively charged by induction. Upon reaching theterminal pulley, the positive charge that has accumulated on the belt isremoved, and the pellets are negatively charged as they leave theterminal pulley and return to the ground pulley.

The Pelletron® device generates a large positive potential within column1954 that is used to accelerate the negative ions of beam 1960. Afterundergoing acceleration in column 1954, beam 1960 passes through chargestripper 1956. Charge stripper 1956 can be implemented as a thin metalfoil and/or a tube containing a gas that strips electrons from thenegative ions, for example. The negatively charged ions are therebyconverted to positively charged ions, which emerge from charge stripper1956. The trajectories of the emerging positively charged ions arealtered so that the positively charged ions travel back throughaccelerating column 1954, undergoing a second acceleration in the columnbefore emerging as positively charged ion beam 1962 from output port1966. Positively charged ion beam 1962 can then be used to treatcellulosic or lignocellulosic material according to the various methodsdisclosed herein.

Due to the folded geometry of accelerator 1950, ions are accelerated toa kinetic energy that corresponds to twice the potential differencegenerated by the Pelletron® charging device. For example, in a 2 MVPelletron® accelerator, hydride ions that are introduced by ion source1952 will be accelerated to an intermediate energy of 2 MeV during thefirst pass through column 1954, converted to positive ions (e.g.,protons), and accelerated to a final energy of 4 MeV during the secondpass through column 1954.

In certain embodiments, column 1954 can include elements in addition to,or as alternatives to, the Pelletron® charging device. For example,column 1954 can include static accelerating elements (e.g., DCelectrodes) and/or dynamic acceleration cavities (e.g., LINAC-typecavities with pulse RF field generators for particle acceleration).Potentials applied to the various accelerating devices are selected toaccelerate the negatively charged ions of beam 1960.

Exemplary tandem accelerators, including both folded and non-foldedaccelerators, are available from National Electrostatics Corporation(Middleton, Wis.), for example.

In some embodiments, combinations of two or more of the various types ofaccelerators can be used to produce ion beams that are suitable fortreating cellulosic or lignocellulosic material. For example, a foldedtandem accelerator can be used in combination with a linear accelerator,a Rhodotron® accelerator, a Dynamitron®, a static accelerator, or anyother type of accelerator to produce ion beams. Accelerators can be usedin series, with the output ion beam from one type of acceleratordirected to enter another type of accelerator for additionalacceleration. Alternatively, multiple accelerators can be used inparallel to generate multiple ion beams. In certain embodiments,multiple accelerators of the same type can be used in parallel and/or inseries to generate accelerated ion beams.

In some embodiments, multiple similar and/or different accelerators canbe used to generate ion beams having different compositions. Forexample, a first accelerator can be used to generate one type of ionbeam, while a second accelerator can be used to generate a second typeof ion beam. The two ion beams can then each be further accelerated inanother accelerator, or can be used to treat cellulosic orlignocellulosic material.

Further, in certain embodiments, a single accelerator can be used togenerate multiple ion beams for treating cellulosic or lignocellulosicmaterial. For example, any of the accelerators discussed herein (andother types of accelerators as well) can be modified to produce multipleoutput ion beams by sub-dividing an initial ion current introduced intothe accelerator from an ion source. Alternatively, or in addition, anyone ion beam produced by any of the accelerators disclosed herein caninclude only a single type of ion, or multiple different types of ions.

In general, where multiple different accelerators are used to produceone or more ion beams for treatment of cellulosic or lignocellulosicmaterial, the multiple different accelerators can be positioned in anyorder with respect to one another. This provides for great flexibilityin producing one or more ion beams, each of which has carefully selectedproperties for treating cellulosic or lignocellulosic material (e.g.,for treating different components in cellulosic or lignocellulosicmaterial).

The ion accelerators disclosed herein can also be used in combinationwith any of the other treatment steps disclosed herein. For example, insome embodiments, electrons and ions can be used in combination to treatcellulosic or lignocellulosic material. The electrons and ions can beproduced and/or accelerated separately, and used to treat cellulosic orlignocellulosic material sequentially (in any order) and/orsimultaneously. In certain embodiments, electron and ion beams can beproduced in a common accelerator and used to treat cellulosic orlignocellulosic material. For example, many of the ion acceleratorsdisclosed herein can be configured to produce electron beams as analternative to, or in addition to, ion beams. For example, Dynamitron®accelerators, Rhodotron® accelerators, and LINACs can be configured toproduce electron beams for treatment of cellulosic or lignocellulosicmaterial.

Moreover, treatment of cellulosic or lignocellulosic material with ionbeams can be combined with other techniques such as sonication. Ingeneral, sonication-based treatment can occur before, during, or afterion-based treatment. Other treatments such as electron beam treatmentcan also occur in any combination and/or order with ultrasonic treatmentand ion beam treatment.

Additives

Any of the many additives used in the manufacture of wood fibercomposites, including but not limited to those listed below, can beadded to or applied to the composites described herein. Additives, e.g.,in the form of a solid or a liquid, can be added to the combination ofcellulosic material (e.g., wood particles or fiber) and resin.

Additives include fillers such as calcium carbonate, graphite,wollastonite, mica, glass, fiber glass, silica, and talc; inorganicflame retardants such as alumina trihydrate or magnesium hydroxide;organic flame retardants such as chlorinated or brominated organiccompounds; ground construction waste; ground tire rubber; carbon fibers;or metal fibers or powders (e.g., aluminum, stainless steel). Theseadditives can reinforce, extend, or change electrical, mechanical and/orcompatibility properties.

Other additives include lignin, fragrances, coupling agents,compatibilizers, e.g., maleated polypropylene, processing aids,lubricants, e.g., fluorinated polyethylene, plasticizers, antioxidants,opacifiers, heat stabilizers, colorants, foaming agents (e.g.,endothermic or exothermic foaming agents), impact modifiers, polymers,e.g., degradable polymers, photostabilizers, biocides, antistaticagents, e.g., stearates or ethoxylated fatty acid amines.

In the case of lignin, lignin can be applied to the wood or wood fiberin a manner so as to penetrate the cellulosic material. In some cases,lignin will cross-link during irradiation, enhancing the properties ofthe irradiated product. In some implementations, lignin is added toincrease the lignin content of a cellulosic material that has arelatively low lignin content in its natural state. In someimplementations, the lignin is dissolved in solvent or a solvent systemand injected into the wood, e.g., under high pressure. The solvent orsolvent system can be in the form of a single phase or two or morephases. Solvent systems for cellulosic and lignocellulosic materialsinclude DMSO-salt systems. Such systems include, for example, DMSO incombination with a lithium, magnesium, potassium, sodium or zinc salt.Lithium salts include LiCl, LiBr, LiI, lithium perchlorate and lithiumnitrate. Magnesium salts include magnesium nitrate and magnesiumchloride. Potassium salts include potassium iodide and nitrate. Examplesof sodium salts include sodium iodide and nitrate. Examples of zincsalts include zinc chloride and nitrate. Any salt can be anhydrous orhydrated. Typical loadings of the salt in the DMSO are between about 1and about 50 percent, e.g., between about 2 and 25, between about 3 and15 or between about 4 and 12.5 percent by weight.

Suitable antistatic compounds include conductive carbon blacks, carbonfibers, metal fillers, cationic compounds, e.g., quaternary ammoniumcompounds, e.g., N-(3-chloro-2-hydroxypropyl)-trimethylammoniumchloride, alkanolamides, and amines. Representative degradable polymersinclude polyhydroxy acids, e.g., polylactides, polyglycolides andcopolymers of lactic acid and glycolic acid, poly(hydroxybutyric acid),poly(hydroxyvaleric acid), poly[lactide-co-(e-caprolactone)],poly[glycolide-co-(e-caprolactone)], polycarbonates, poly(amino acids),poly(hydroxyalkanoate)s, polyanhydrides, polyorthoesters and blends ofthese polymers.

When the above additives are included, they can be present in amounts,calculated on a dry weight basis, of from below about 1 percent to ashigh as about 15 percent, based on total weight of the fibrous material.More typically, amounts range from between about 0.5 percent to about7.5 percent by weight.

Any additives described herein can be encapsulated, e.g., spray dried ormicroencapsulated, e.g., to protect the additives from heat or moistureduring handling.

The fibrous materials, densified fibrous materials, resins, or additivescan be dyed. For example, the fibrous material can be dyed beforecombining with the resin and compounding to form composites. In someembodiments, this dyeing can be helpful in masking or hiding the fibrousmaterial, especially large agglomerations of the fibrous material, inmolded or extruded parts, when this is desired. Such largeagglomerations, when present in relatively high concentrations, can showup as speckles in the surfaces of the molded or extruded parts.

For example, the desired fibrous material can be dyed using an acid dye,direct dye, or a reactive dye. Such dyes are available from SpectraDyes, Kearny, N.J. or Keystone Aniline Corporation, Chicago, Ill.Specific examples of dyes include SPECTRA™ LIGHT YELLOW 2G, SPECTRACID™YELLOW 4GL CONC 200, SPECTRANYL™ RHODAMINE 8, SPECTRANYL™ NEUTRAL RED B,SPECTRAMINE™ BENZOPERPURINE, SPECTRADIAZO™ BLACK OB, SPECTRAMINE™TURQUOISE G, and SPECTRAMINE™ GREY LVL 200%, each being available fromSpectra Dyes.

In some embodiments, resin color concentrates containing pigments areblended with dyes. When such blends are then compounded with the desiredfibrous material, the fibrous material may be dyed in-situ during thecompounding. Color concentrates are available from Clariant.

It can be advantageous to add a scent or fragrance to the fibrousmaterials or composites. For example, it can be advantageous for thecomposites to smell and/or look like natural wood, e.g., cedar. Forexample, the fragrance, e.g., natural wood fragrance, can be compoundedinto the resin used to make the composite. In some implementations, thefragrance is compounded directly into the resin as an oil. For example,the oil can be compounded into the resin using a roll mill, e.g., aBanbury® mixer or an extruder, e.g., a twin-screw extruder withcounter-rotating screws. An example of a Banbury® mixer is the F-SeriesBanbury® mixer, manufactured by Farrel. An example of a twin-screwextruder is the WP ZSK 50 MEGAcompunder™, manufactured by Krupp Werner &Pfleiderer. After compounding, the scented resin can be added to thefibrous material and extruded or molded. Alternatively, master batchesof fragrance-filled resins are available commercially from InternationalFlavors and Fragrances, under the tradename PolyIff™ or from the RTPCompany. In some embodiments, the amount of fragrance in the compositeis between about 0.005% by weight and about 2% by weight, e.g., betweenabout 0.1% and about 1%.

Other natural wood fragrances include evergreen or redwood. Otherfragrances include peppermint, cherry, strawberry, peach, lime,spearmint, cinnamon, anise, basil, bergamot, black pepper, camphor,chamomile, citronella, eucalyptus, pine, fir, geranium, ginger,grapefruit, jasmine, juniper berry, lavender, lemon, mandarin, marjoram,musk, myrrh, orange, patchouli, rose, rosemary, sage, sandalwood, teatree, thyme, wintergreen, ylang ylang, vanilla, new car or mixtures ofthese fragrances. In some embodiments, the amount of fragrance in thefibrous material-fragrance combination is between about 0.005% by weightand about 20% by weight, e.g., between about 0.1% and about 5% or 0.25%and about 2.5%.

Suitable fillers include, for example, inorganic fillers such as calciumcarbonate (e.g., precipitated calcium carbonate or natural calciumcarbonate), aragonite clay, orthorhombic clays, calcite clay,rhombohedral clays, kaolin, clay, bentonite clay, dicalcium phosphate,tricalcium phosphate, calcium pyrophosphate, insoluble sodiummetaphosphate, precipitated calcium carbonate, magnesium orthophosphate,trimagnesium phosphate, hydroxyapatites, synthetic apatites, alumina,silica xerogel, metal aluminosilicate complexes, sodium aluminumsilicates, zirconium silicate, silicon dioxide or combinations of theinorganic additives may be used. The fillers can have, e.g., a particlesize of greater than 1 micron, e.g., greater than 2 micron, 5 micron, 10micron, 25 micron or even greater than 35 microns.

Nanometer scale fillers can also be used alone, or in combination withfibrous materials of any size and/or shape. The fillers can be in theform of, e.g., a particle, a plate or a fiber. For example, nanometersized clays, silicon and/or carbon nanotubes, and silicon and/or carbonnanowires can be used. The filler can have a transverse dimension lessthan 1000 nm, e.g., less than 900 nm, 800 nm, 750 nm, 600 nm, 500 nm,350 nm, 300 nm, 250 nm, 200 nm, less than 100 nm, or even less than 50nm.

In some embodiments, the nano-clay is a montmorillonite. Such clays areavailable from Nanocor, Inc. and Southern Clay products, and have beendescribed in U.S. Pat. Nos. 6,849,680 and 6,737,464. The clays can besurface treated before mixing into, e.g., a resin or a fibrous material.For example, the clay can be surface is treated so that its surface isionic in nature, e.g., cationic or anionic.

Aggregated or agglomerated nanometer scale fillers, or nanometer scalefillers that are assembled into supramolecular structures, e.g.,self-assembled supramolecular structures can also be used. Theaggregated or supramolecular fillers can be open or closed in structure,and can have a variety of shapes, e.g., cage, tube or spherical.

Process Water

In the processes disclosed herein, whenever water is used in anyprocess, it may be grey water, e.g., municipal grey water, or blackwater. In some embodiments, the grey or black water is sterilized priorto use. Sterilization may be accomplished by any desired technique, forexample by irradiation, steam, or chemical sterilization.

EXAMPLES

The following examples are not limiting of the invention recited in theclaims.

Example 1 Methods of Determining Molecular Weight of Cellulosic andLignocellulosic Materials by Gel Permeation Chromatography

This example illustrates how molecular weight is determined for thematerials discussed herein. Cellulosic and lignocellulosic materials foranalysis were treated as follows:

A 1500 pound skid of virgin bleached white Kraft board having a bulkdensity of 30 lb/ft³ was obtained from International Paper. The materialwas folded flat, and then fed into a 3 hp Flinch Baugh shredder at arate of approximately 15 to 20 pounds per hour. The shredder wasequipped with two 12 inch rotary blades, two fixed blades and a 0.30inch discharge screen. The gap between the rotary and fixed blades wasadjusted to 0.10 inch. The output from the shredder resembled confetti(as above). The confetti-like material was fed to a Munson rotary knifecutter, Model SC30. The discharge screen had ⅛ inch openings. The gapbetween the rotary and fixed blades was set to approximately 0.020 inch.The rotary knife cutter sheared the confetti-like pieces across theknife-edges. The material resulting from the first shearing was fed backinto the same setup and the screen was replaced with a 1/16 inch screen.This material was sheared. The material resulting from the secondshearing was fed back into the same setup and the screen was replacedwith a 1/32 inch screen. This material was sheared. The resultingfibrous material had a BET surface area of 1.6897 m²/g +/−0.0155 m²/g, aporosity of 87.7163 percent and a bulk density (@0.53 psia) of 0.1448g/mL. An average length of the fibers was 0.824 mm and an average widthof the fibers was 0.0262 mm, giving an average L/D of 32:1.

Sample materials presented in the following Tables 1 and 2 below includeKraft paper (P), wheat straw (WS), alfalfa (A), and switchgrass (SG).The number “132” of the Sample ID refers to the particle size of thematerial after shearing through a 1/32 inch screen. The number after thedash refers to the dosage of radiation (MRad) and “US” refers toultrasonic treatment. For example, a sample ID “P132-10 ” refers toKraft paper that has been sheared to a particle size of 132 mesh and hasbeen irradiated with 10 MRad.

TABLE 1 Peak Average Molecular Weight of Irradiated Kraft Paper SampleSample Dosage¹ Average MW ± Std Source ID (MRad) Ultrasound² Dev. KraftP132 0 No 32853 ± 10006 Paper P132-10  10 ″  61398 ± 2468** P132-100 100″ 8444 ± 580  P132-181 181 ″ 6668 ± 77  P132-US  0 Yes 3095 ± 1013 **Lowdoses of radiation appear to increase the molecular weight of somematerials ¹Dosage Rate = 1 MRad/hour ²Treatment for 30 minutes with 20kHz ultrasound using a 1000 W horn under re-circulating conditions withthe material dispersed in water.

TABLE 2 Peak Average Molecular Weight of Irradiated Materials Dosage¹Average MW ± Std Sample ID Peak # (MRad) Ultrasound² Dev. WS132 1 0 No1407411 ± 175191  2 ″ ″ 39145 ± 3425  3 ″ ″ 2886 ± 177  WS132-10*  1 10″ 26040 ± 3240  WS132-100* 1 100 ″ 23620 ± 453  A132 1 0 ″ 1604886 ±151701  2 ″ ″ 37525 ± 3751  3 ″ ″ 2853 ± 490  A132-10*  1 10 ″ 50853 ±1665  2 ″ ″ 2461 ± 17  A132-100* 1 100 ″ 38291 ± 2235  2 ″ ″ 2487 ± 15 SG132 1 0 ″ 1557360 ± 83693  2 ″ ″ 42594 ± 4414  3 ″ ″ 3268 ± 249 SG132-10*  1 10 ″ 60888 ± 9131  SG132-100* 1 100 ″ 22345 ± 3797 SG132-10-US 1 10 Yes 86086 ± 43518 2 ″ ″ 2247 ± 468  SG132-100- 1 100 ″4696 ± 1465 US *Peaks coalesce after treatment **Low doses of radiationappear to increase the molecular weight of some materials ¹Dosage Rate =1 MRad/hour ²Treatment for 30 minutes with 20 kHz ultrasound using a1000 W horn under re-circulating conditions with the material dispersedin water.

Gel Permeation Chromatography (GPC) is used to determine the molecularweight distribution of polymers. During GPC analysis, a solution of thepolymer sample is passed through a column packed with a porous geltrapping small molecules. The sample is separated based on molecularsize with larger molecules eluting sooner than smaller molecules. Theretention time of each component is most often detected by refractiveindex (RI), evaporative light scattering (ELS), or ultraviolet (UV) andcompared to a calibration curve. The resulting data is then used tocalculate the molecular weight distribution for the sample.

A distribution of molecular weights rather than a unique molecularweight is used to characterize synthetic polymers. To characterize thisdistribution, statistical averages are utilized. The most common ofthese averages are the “number average molecular weight” (M_(n)) and the“weight average molecular weight” (M_(w)).

M_(n) is similar to the standard arithmetic mean associated with a groupof numbers. When applied to polymers, M_(n) refers to the averagemolecular weight of the molecules in the polymer. M_(n) is calculatedaffording the same amount of significance to each molecule regardless ofits individual molecular weight. The average M_(n) is calculated by thefollowing formula where N_(i) is the number of molecules with a molarmass equal to M_(i). Methods of calculating these values are describedin the art, e.g., in Example 9 of WO 2008/073186.

The polydispersity index or PI is defined as the ratio of M_(w)/M_(n).The larger the PI, the broader or more disperse the distribution. Thelowest value that a PI can be is 1. This represents a monodispersesample; that is, a polymer with all of the molecules in the distributionbeing the same molecular weight.

The peak molecular weight value (M_(P)) is another descriptor defined asthe mode of the molecular weight distribution. It signifies themolecular weight that is most abundant in the distribution. This valuealso gives insight to the molecular weight distribution.

Most GPC measurements are made relative to a different polymer standard.The accuracy of the results depends on how closely the characteristicsof the polymer being analyzed match those of the standard used. Theexpected error in reproducibility between different series ofdeterminations, calibrated separately, is ca. 5-10% and ischaracteristic to the limited precision of GPC determinations.Therefore, GPC results are most useful when a comparison between themolecular weight distribution of different samples is made during thesame series of determinations.

The lignocellulosic samples required sample preparation prior to GPCanalysis. First, a saturated solution (8.4% by weight) of lithiumchloride (LiCl) was prepared in dimethyl acetamide (DMAc). Approximately100 mg of each sample was added to approximately 10 g of a freshlyprepared saturated LiCl/DMAc solution, and the mixtures were heated toapproximately 150° C.-170° C. with stirring for 1 hour. The resultingsolutions were generally light- to dark-yellow in color. The temperatureof the solutions was decreased to approximately 100° C. and thesolutions were heated for an additional 2 hours. The temperature of thesolutions was then decreased to approximately 50° C. and the samplesolutions were heated for approximately 48 to 60 hours. Of note, samplesirradiated at 100 MRad were more easily solubilized as compared to theiruntreated counterpart. Additionally, the sheared samples (denoted by thenumber 132) had slightly lower average molecular weights as comparedwith uncut samples.

The resulting sample solutions were diluted 1:1 using DMAc as solventand were filtered through a 0.45 μm PTFE filter. The filtered samplesolutions were then analyzed by GPC. The peak average molecular weight(Mp) of the samples, as determined by Gel Permeation Chromatography(GPC), are summarized in Tables 1 and 2. Each sample was prepared induplicate and each preparation of the sample was analyzed in duplicate(two injections) for a total of four injections per sample. The EasiCal®polystyrene standards PS1A and PS1B were used to generate a calibrationcurve for the molecular weight scale from about 580 to 7,500,00 Daltons.The GPC analysis conditions are recited in Table 3 below.

TABLE 3 GPC Analysis Conditions Instrument: Waters Alliance GPC 2000Plgel 10 μ Mixed-B Columns (3): S/N's: 10M-MB-148-83; 10M-MB-148-84;10M-MB-174-129 Mobile Phase (solvent): 0.5% LiCl in DMAc (1.0 mL/min.)Column/Detector Temperature: 70° C. Injector Temperature: 70° C. SampleLoop Size: 323.5 μL

Example 2 Radiation Treatment of Boxwood Samples

Boxwood boards, ⅛ inch thick, were treated with electron beam radiation(a 5 MeV beam), at dosages from 1 MRad to 100 MRads, with the numbernext to the “B” in the Tables below indicating the dosage received(e.g., B means a board that was not irradiated, B1 means a board thatreceived 1 MRad, and B10 means a board that received 10 MRads.) Theflexural strength of the boards was then tested using ASTM D 790 and D143 (cross head speed was 0.1 inch/min and span/thickness was 14:1), andthe tensile strength was tested using ASTM D 638 (using Type I specimensand a cross head speed of 0.2 inch/min). The results of this testing areshown in Tables I and II, below.

TABLE I Summary of Test Results - Flexural Strength SampleIdentification Average Flexural Strength (psi) Individual Values B 1160010800, 11900, 10800, 12000, 12600 B1 13300 13600, 12700, 13800, 13300 B320200 21400, 20000, 18700, 20700 B5 16500 16100, 15600, 16700, 17600 B710700 11700, 11200, 8920, 10900 B10 10900 10200, 11100, 11900, 10300 B1512500 14900, 10200, 13800, 11000 B20 6420 5770, 6390, 6800, 6720 B307050 6160, 8240, 5910, 7880 B70 4200 4240, 4540, 3560, 4460 B100 28203020, 3120, 2790, 2350

TABLE II Summary of Test Results - Tensile Strength Sample TensileStrength (psi) Identification Average Individual Values B 5760 4640,7000, 5310, 6110 B1 7710 8020, 7560, 6280, 8980 B3 3960 3840, 3880,4480, 3640 B5 8470 7540, 8890, 8910, 8530 B7 5160 5660, 4560, 6850, 3570B10 2870 2370, 3800, 3860, 2530 B15 2170 2160, 2380, 2040, 2080 B20 26302890, 2530, 2610, 2470 B30 5890 6600, 5390, 5910, 5660 B70 1840 1490,2290, 2010, 1570 B100 1720 1860, 1840, 1620, 1550

Example 3 Preparation of Sheared Fibrous Material From Bleached KraftBoard

A 1500 pound skid of virgin bleached white Kraft board having a bulkdensity of 30 lb/ft³ was obtained from International Paper. The materialwas folded flat, and then fed into a 3 hp Flinch Baugh shredder at arate of approximately 15 to 20 pounds per hour. The shredder wasequipped with two 12 -inch rotary blades, two fixed blades and a 0.30-inch discharge screen. The gap between the rotary and fixed blades wasadjusted to 0.10 -inch. The output from the shredder resembled confetti.The confetti-like material was fed to a Munson rotary knife cutter,Model SC30. The discharge screen had ⅛-inch openings. The gap betweenthe rotary and fixed blades was set to approximately 0.020 inch. Therotary knife cutter sheared the confetti-like pieces across theknife-edges. The material resulting from the first shearing was fed backinto the same setup and the screen was replaced with a 1/16-inch screen.This material was sheared. The material resulting with a 1/32-inchscreen. This material was sheared. The resulting fibrous material had aBET surface area of 1.6897 m²/g+/−0.0155 m²/g, a porosity of 87.7163percent and a bulk density (@0.53 psia) of 0.1448 g/mL. An averagelength of the fibers was 0.824 mm and an average width of the fibers was0.0262 mm, giving an average L/D of 32:1.

Example 4 Electron Beam Processing of Untreated Wood and Fiber/resinComposites

Composites 0.5-inches thick that included 50 percent by weight of theKraft fiber of Example 3 and polyethylene were prepared according to theprocedures outlined in “FIBROUS MATERIALS AND COMPOSITES,”PCT/US2006/010648, filed on Mar. 23, 2006. Whitewood boards that werenominally 0.5-inches thick were purchased from the Home Depot. Thesamples were treated with a beam of electrons using a Rhodotron® TT200continuous wave accelerator delivering 5 MeV electrons at 80 kW outputpower. Table 4 describes the nominal parameters for the TT200. Table 5reports the nominal doses (in MRad) and actual doses (in kgy) deliveredto the samples.

TABLE 4 Rhodotron ® TT 200 Parameters Beam Beam Produced: Acceleratedelectrons Beam energy: Nominal (maximum): 10 MeV (+0 keV-250 keV Energydispersion at 10 Mev: Full width half maximum (FWHM) 300 keV Beam powerat 10 MeV: Guaranteed Operating Range 1 to 80 kW Power ConsumptionStand-by condition  <15 kW (vacuum and cooling ON): At 50 kW beam power:<210 kW At 80 kW beam power: <260 kW RF System Frequency: 107.5 ± 1 MHzTetrode type: Thomson TH781 Scanning Horn Nominal Scanning Length 120 cm(measured at 25-35 cm from window): Scanning Range: From 30% to 100% ofNominal Scanning Length Nominal Scanning Frequency 100 Hz ± 5% (at max.scanning length): Scanning Uniformity (across 90% ± 5% of NominalScanning Length)

TABLE 5 Dosages Delivered to Samples Total Dosage (MRad) (NumberAssociated with Sample ID Delivered Dose (kgy)¹ 1 9.9 3 29.0 5 50.4 769.2 ¹For example, 9.9 kgy was delivered in 11 seconds at a beam currentof 5 mA and a line speed of 12.9 feet/minute. Cool time between 1 MRadtreatments was about 2 minutes.

All samples were stiffer to the touch than untreated controls, butotherwise appeared visibly identical to the controls.

Other Embodiments

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

1. A method of treating wood, the method comprising: irradiating woodhaving a first molecular weight with electron beam radiation whilecontrolling a gas blanketing the wood through which the electron beampasses, electrons of the beam having an energy of about 0.5 to about 5MeV, to provide treated wood, in the form of sawn lumber or a finishedwood product selected from the group consisting of solid wood objectsand plywood, in which a cellulosic component of the wood has a second,relatively higher molecular weight at least about 10% higher than thefirst weight.
 2. The method of claim 1, wherein the gas blanketing thewood comprises a gas selected from the group consisting of nitrogen,oxygen, ozone, nitrogen dioxide, sulfur dioxide, and chlorine.
 3. Themethod of claim 1, further comprising quenching the irradiated wood. 4.The method of claim 3, wherein quenching is performed in the presence ofa gas selected to react with radicals present in the irradiated wood. 5.The method of claim 1, wherein the increase in molecular weight is atleast 50%.
 6. The method of claim 1 wherein irradiating comprisesirradiating multiple times.
 7. The method of claim 1 wherein the woodhas multiple sides and irradiating comprises irradiating more than oneside of the wood.
 8. The method of claim 1 wherein the wood isirradiated at a dose rate of at least 0.5 Mrad/s.
 9. The method of claim8 wherein the wood is irradiated at a dose rate of at least 1 Mrad/sec.10. The method of claim 1 wherein the wood product comprises plywood.